Electric furnace.



E. F. coLLLNs.

ELEGIRIC FURNACE. APPLlcATLoN FILED APR.17. 1914.

1,156,668. I Patented oct. 12, 1915.

2 SHEETS-SHEET l.A

Witnesses: inventor;

/57 Edgar P col uns,

E. F. COLLINS.

ELECTRIC FURNACE.

APPLICATION FILED APR. 11. 1914.

-.1,156.668. Patented 0111.121915.

' 2 SHEETS-SHEET 2..

Witnesses 1 Inventor: @L M4, A Ed ar FT Colins, f b9 /cz'm Hls Dcttovrjeg- UNITED sTATEs PATENT oEErcE EDGAR F.. COLLINS, 0F SCHENECTADY, NEW YORK, SSIGNOR TO GENERAL ELECTRIC.

` COMPANY, A CORPORATION OF VNEW YORK. L i

ELECTRIC FURNACE.

To all whom t may concern.' A

Be it knowny that I, lEDGAR F. COLLINS, a citizen ofv the United States,` residing at Schenectady, in the .county of Schenectady,

State of New York, have linvented certain new and useful Improvements in Electric Furnaces, of which the following is a specification. x v

The present invention relates to electric furnaces of the resistance type and its o b ject is to provide a rugged, reliable furnace suitable for' continuous operation for industrial purposes, such, for example, as the heating of metallic articles preliminary to forging or tempering.

Furnaces of this character require a properly distributed and lsteadily maintained temperature in the heating zone and considerable heat capacity so that the furnace temperature'will not be unduly lowered by insertion of cold objects.

Resistance furnaces provided with a heating space containing abed of resistance material serving' as a heati-ng means are known and it has also been suggested to construct an arch spanning the heating space as the resistor, but in each of these cases heat has been imparted to the articles to be heated from one direction only. Such la construe# tion while operative for some purposes 1s not suited for a furnace into which articles to be heated are being continually inserted and Withdrawn, as the cooling effect ofthe top or bottom of the furnace lengthens the time necessary for the articles to attain the desired'temperature andv produces unequal heating.

My invention provides a furnace in which an extended Zone may be uniformly maintained at a required high temperature by radiation both from below and above, and the temperature distribution or gradient may bel controlled in accordancey with the requirements of the service. The electrical contact to the tw@ heaters is made through the medium of finely divided conducting material contained in upwardly extending channels. The various novel features of my invention are pointed out with greater particularity in the l'appended claims.

In the accompanying drawings Figure 1 A is a generalperspective view of a furnace embodying my invention; Fig. 2 is a longitudinal section taken through line 2-2 of Fig. 3 which is a cross-section at right an- Specication of Letters Patent. Patented-'Oct 12, 191.5. .Application led April 17, 1914. Serial No. 832,489.

gles theretoyandFig. 4 is a section taken ori-lines 444 through the arch above the heating space.,

As sl'iown'particularly in Figs. 1 and 2, the main heating space i of the furnace is surrounded by fire-brick walls 2 supported by structural steel vframe work Access to .the heat zone is afforded by opening 4 which may be closed by a door 5 operated by means of a gear including the lever 6 and counter-weight 7.

The heat is inipart generated in a granui lar resistor 8 and part in a conductive arch 9 located above the-granular resistor. The granular resistor preferably consists of lumps of coke or similar carbonaceousma-` -ter1al, the lumps being about to inch 4carborundumwith asticky carbonaceous binder. The. arch 9 is supported by the fire brick side walls of the furnace as shown in Figs. 3 and 4 by fire bricks 11 and 11. In order to increase the resistance of the arch and also to predetermine the amount f heat generated therein, the carborundum brick may be laidr so as to cause the current to pass in a sinuous ypath from one row to another as shown in Fig. 4. For this purpose no mortar is placed between the abutting ends of the brick while the sides of the adjacent rows are joined by a suitable cement or mor; tar such as finely divided carborundum and a binder. The size of the brick is adjusted so that adjacent bricks will overlap, or if a.

still higher resistance is required as, for example, for thepart of the heating chamber` farthest removed from the door` which. is least subjected to cooling, two rows of brick may be laid with their ends adj acent-but not cemented as shown at 12, Fig..v 4, so as t0 still more increase the resistance. If desired the side walls mayalso be constituted of carborundum' .or other highly `refractory material having a resistance of the same order of magnitude as carbon.

Contact is made both to the granular resistor and to the conducting arch by upwardly extending columns 13, 14, of conl ducting materialmore finely divided and,

therefore, of greater electrical conductivitythan the granular resistor. prefer to use for this purpose carbonaceous material, for example, coke, which has 'been powdered fine enough to pass through a screen having about 80 meshes to the square inch. These columns of carbonaceous material are` supported by the walls 'of the furnace-and by arches 1,5, 16 at the ends of the furnaces, best shown in Fig. 2. Above these arches is a layer of refractory material, as shown at 17, Fig. 8, which may be similar in character to the hearth 10, namely, carborundum sand compacted with a'fbinder of water glass. A similar layer of carborundum fire sand is placed above the heating arch 9 as shown at 18, Fig. 3, for the purpose of conserving the heat generated in the arch. Current is introduced by carbon'electrodesI 19, 20, 21 and 22, whiph are embedded in the columns of powdered coke. Some of the advantages of Y this arrangement for introducing the heat- 'ing current are as follows: The current being introduced from above causes a maximum heating effect to be 'jobtained in the upper layers of the granular resistor thus v'protecting the lbed-plate and causing the maximum heat to be obtained where it is needed, namely, nearest the worlrv to be heated. The electrodes being laterally movable gravity. This powdered material must bev 'i replenished from time to time as it is gradually fed down into the heating zone of the as indicated in the drawing.

furnace where it mixes to some extent with the coarsely granular material near the ends My experience has shown that when material as coarsely granular as that used in the heating resistor is packed around the electrodes that they vaperate at such high temperature as to render their life very short. Electrical contact is made to the projecting ends of the electrodes by copper plates 23 pressed against the sides of theelectrodes by clamps 24. A suitable form'of electrical terminal is indicated at 25.

I haveA found in a furnace as above constructed in which the heating arch is proportioned to carry about 30 to L10% of the total energy that temperatures up to about 1500o to 1600o can be steadily anduniformly maintained throughout the heating zone. Ordinarily when the furnace is used for forging copper the temperature may be only about 900o C. and for ,forging steel about 1200o C. and I have-found by a long continued series of experiments in practical experience with the furnace that these temperatures can be accurately maintained with only such care as may be given the furnace by the workman engaged in the forge-shop.

What I claim as new and desire to secure by Letters Patent of the United States, is

l. An electric furnace comprising walls of refractory materials inclosing a heating chamber, a heater of refractory material on the floor of said chamber, the upper wall of said chamber consisting of diflicultly oxidizable refractory material having a higher resistance when cold than said floor .heater and having a negative temperature resistance coefficient, constituting a heater over heaters.

2. In an electric furnace, the combination of a heater of granular conductive material,

vertical channels at each end of said heater,

'90 said chamber, and commonmeans for passving electrical energy through both said ing each of said electrodes respectively to l the heater.

l.v An electric furnace comprising a refractory hearth, a refractory conductive granular material on said hearth, refractory walls'inclosing the hearth, the upper wall being in part conducting and containing up- 4 wardly extending channels, a refractory conductive material in said channels more finely'comminuted than the material on said hearth and electrically contacting therewith and electrodes transversely movable in said channels embedded in said finely commilnuted material.-

5. An electric furnace comprising a refractory hearth, lump shaped carbonaceous material on said hearth, .walls of refractory compound containing silicon and carbon inclosing a space above said hearth the upper;

wall being in part conducting and containing upwardly-extending channels, nely ccmlninuted carbonaceous material passing through a screen having about 80 meshes to the square inch ,in'said channels contacting with the naterifal'on said. hearth and a pluf.

rality of electrodes embedded in the 'material in said channels.` I

6. In an electric furnace, a heater comprising rows Vof shaped pieces of resistance material, the sides of adjacent pieces being arranged to overlap each other, and a conductmy hand this 16th day of April, 1914.

EDGAR F. COLLINS.

Witnesses:

E. J. VAN WIE, HELEN ORFORD.

Copies ot this patent niay'be obtained' for ye cents each, by addressing the Commissioner of Patents,

Washington, D. C. 

